1. Field of the Invention
Fungal wilt diseases cause reduction in both the quality and quantity of major agricultural crops resulting in substantial economic losses each year. In particular, verticillium wilt caused by the infection of the plant's root and vascular system by Verticillium dahliae severly affects potatoes, cotton, and many other important crop plants. Control of Verticillium dahliae is problematic because of its persistence in the soil and its endophytic location in the root system of the plant. Although a number of control techniques have been suggested, such as soil fumigation, crop rotation, resistant cultivars, and use of new planting locations uninfected by the fungus, none have been entirely successful. Soil fumigation is prohibitively expensive, pollutes the environment, and must be periodically repeated. Rotation with non-susceptible crops will reduce the fungal infestation, but suitable alternate crops provide an inadequate economic return. Finally, the amount of useful farmland is limited which provides a strong disincentive to unecomonic utilization.
It would thus be desirable to provide an effective biological control which inhibits verticillium wilt in a safe and economic manner, while maintaining land productivity.
2. Description of the Prior Art
Wadi (1982) "Biological Control of Verticillium dahliae on Potato" (Ph.D. Thesis) Washington State University, Department of Plant Pathology, describes the use of particular strains of Cellulomonas flavigena, Pseudomonas fluorescens, and Streptomyces flavofungini for the control of verticillium wilt on potatoes. U.S. Department of Agriculture publication ARS-S-19 (December 1973) entitled "Verticillium Wilt of Cotton" describes various biological and chemical control schemes, including crop rotation, soil fumigation, systemic fungicides, systemic insecticides, and growth regulators. The biological control of vascular wilt fungi is discussed in Baker: "Biological Control" in Fungal Wilt Diseases of Plants, Chapter 14, Academic Press, New York (1981) pp. 523-561; and Kommedahl and Windels: "Introduction of Microbial Antagonists to Specific Courts of Infection: Seeds, Seedlings and Wounds" in Bettsville Symposia in Agriculture Research [5] Biological Control in Crop Production, Allanhead, Osmun, Grandida, London, Toronto, Sydney, pp. 226-248. Marois (1982) Plant Disease 66:1166-1168 describes the treatment of plant roots with Taleromyces flavus to treat verticillium wilt in eggplant.